This invention concerns the installation of pipes to replace existing underground pipes.
The underground pipes which are to be replaced by the method are relatively small diameter pipes which carry gas or water, for example the service pipe from a main pipe to a consumer, such as a household. Such pipes may be of lead, galvanised steel or plastics, but a particular application for the invention is the replacement of underground lead pipes which ate service pipes carrying water from a main to a consumer.
The are several reasons why it is desirable that lead service pipes should be replaced, including that the ingestion of too much lead is poisonous, and whilst legislation currently allows 0.7 mg/liter in water for drinking purposes, and lead extraction from water pipes falls within this limit, current trends suggest that the limit will be reduced to 0.2
mg/liter, which is less than the current lead levels in drinking water. The lead pipes will therefore have to be replaced, or put out of use, by the installation of a new pipe alongside the old lead pipe.
Secondly, the lead pipes are relatively old (no new lead pipes have been installed for the last 40 years) and many of them are leaking, which means that water is being lost. With water becoming mote important in terms of preservation, this leakage problem must be and is being addressed by water companies. An effective means of reducing the leakage is desired. Replacement of the lead pipes forms a means for achieving this.
The present invention concerns the replacement of pipes by a method and/or means which can put existing lead pipes out of use, and thereby address the leakage problem.
Methods of replacing larger underground pipes have been already proposed, but these suffer from size limitations. For example it is known to pull cutting devices through larger diameter pipes to cut the old pipe along a longitudinal line using a towing cable attached to the front of the cutting device, followed by spreading the slit pipe by means of a former, to the rear of which a new pipe is attached, so that as the former moves along the line of the old pipe, the new pipe is inserted. The known method is suitable for larger diameter pipes in the order of 50 to 250 mm diameter, but the method does not directly scale down to make it suitable for the replacement of water and gas service pipes which are in the order of 30 mm or less.
The present invention also makes use of a cutting device comprising a former and a cutting blade, the blade serving to slit the existing pipe and the former to spread the slit pipe, as the device is pulled along the line of the pipe by a towing cable which is threaded into the existing pipe, and a new pipe is inserted by being attached to the rear of the former, the method in addition comprising using a towing cable which is a relatively neat fit in the bore of the existing pipe, and couples to the cutting device at a position to the rear of the cutting blade, so that the cable in effect pushes the cutting blade along the line of the existing pipe.
This has a significant advantage in the case of small pipes, in that, in size terms, the coupling of the cable to the device is not constrained as it would be if the end of the cable were to be ahead of the cutting blade, as that attachment would have to pass into the bore of the existing pipe ahead of the cutting blade. This would make cutting of small diameter pipes impossible.
In a preferred method, the end of the cable is coupled to the cutting device by being provided with an enlarged portion, for example provided by a ferrule, which is clamped on to the end of the cable and the former has a recess in which the ferrule is received, so that the presence of the ferrule does not alter the outer profile of the former, which should be smooth to perform the spreading of the slit pipe.
Preferably, the former has a passage leading from the front end to the recess, and the cable is coupled to the former by being threaded through the recess and then the passage until the ferrule seats on a shoulder of the recess and can go no further. The cable emerges from the front end of the former and into the pipe to be slit and replaced. The construction of the rear of the former, and the means of attachment of the new replacement pipe may be conventional, as is the nature of the new pipe, which preferably is of polyethylene.
Inside the passage there is preferably a rigid sleeve through which the cable passes, such sleeve serving as a means for providing a supporting reaction to the cutting blade as it cuts through the existing pipe, rather than the reaction being taken by the cable.
As to the cable being a relatively neat fit in the existing pipe, this is important for cable being sufficiently large to withstand the loads involved, but the cable also has to pass through the pipe without snagging. Although the cable can snag if it is too neat a fit, it can also snag if the fit is not sufficiently neat, and it may break under increased load. In this connection, the existing service pipes usually ate not perfectly straight, and often have curves, and rises and falls.
In the use of the method, the former which has a small front end which can enter the bore of the existing pipe, is forced, by pulling the cable where it projects from the remote end of the existing pipe, into the bore of the pipe. Eventually, the cutting blade engages the pipe and starts to slit the pipe. The larger rear of the former then enters the pipe and starts to spread it. The former moves along the line of the pipe, pulling in the replacement pipe. In fact, the part of the former in front of the ferrule in the recess, which includes the cutting blade, is pushed by the ferrule along the line of the pipe. Thus the existing pipe is spread ahead of the ferrule, and so there is no interference between the ferrule and the existing pipe, due to the method and means of the invention.
The invention also extends to the provision of a cutting device and a pulling cable combination by which the method can be performed.